1. Field of the Invention
The present invention relates to a rotary connector for connecting two relatively rotating members.
2. Description of the Related Art
In a rotary connector for connecting relatively rotating members, e.g., a rotary connector used in a steering apparatus of an automobile, a flat cable is used in order to improve the reliability of electrical connection with the vehicle-body side. This flat cable is a flexible belt-shaped cable which is formed by coating a plurality of flat square conductors for insulation. The flat cable is housed in the form of a spiral in an annular space defined by a rotating case and a stationary case.
The rotary connector, containing the flat cable therein, transmits the rotatory force of a steering shaft, which is produced by turning a steering wheel, to the rotating case through a torque transmission section which comprises a key or pin on the connector. Thus, the rotary connector is designed so that the rotation of the steering wheel is absorbed by a tightening or loosening action of the flat cable as the rotating case rotates, whereby electrical connection with external equipment can be established.
In the rotary connector constructed in this manner, the allowable range of rotation of the rotating case with respect to the stationary case depends on the length of the flat cable. That is, the rotational range is limited.
In mounting the rotary connector in a vehicle, therefore, it is necessary to adjust the steering wheel to a straight-advance position and to orient the rotary connector to a neutral position of the tightening or loosening of the flat cable with respect to horizontal rotation. Thus, the rotary connector must be mounted in the vehicle in a manner such that the flat cable can tighten or loosen within the allowable range of rotation even when the steering wheel is turned to its structural motion limit.
If the rotary connector is mounted in the vehicle without fulfilling these requirements, the flat cable tightens to its limit in the middle of the steering wheel operation, thereby hindering smooth rotation of the steering wheel.
Accordingly, the conventional rotary connector is separately provided with a cutting device in the form of a cutting edge, as a measure to counter the above situation, such that the cutting device cuts the flat cable to eliminate the hindrance to the rotation of the steering wheel.
Each flat cable has its own strength depending on the specifications, including the number and sectional area of conductors which vary according to the application of the rotary connector. According to the method in which the hindrance to the rotation of the steering wheel is eliminated by cutting the flat cable, therefore, the cutting torque must be changed for each cable, which is hardly feasible.
With the diversification of modern vehicles, in particular, the rotary connector tends to use an increased number of circuits, and cutting the flat cable requires a very large torque. In consideration of the durability of the flat cable, therefore, it is not advisable to use a sharp cutting device. If the cutting device is a dull one, however, it cannot successfully cut the flat cable. Thus, it is delicate to adjust the cutting device to cutting work under a proper torque.
Further, the use of the cutting device or cutting edge in the rotary connector means an increase in the number of components of the connector, so that the space for the flat cable is reduced. In order to secure the same amount of rotation, therefore, the rotary connector itself is expected to be large-sized.